The present invention relates to cementing operations and, more particularly, in certain embodiments, to sealant compositions that comprise cement kiln dust (“CKD”) and tire-rubber particles and associated methods of use in servicing well bores.
In cementing methods, such as well construction and remedial cementing, sealant compositions are commonly utilized. As used herein, the term “sealant composition” refers to a composition(s) that hydraulically sets or otherwise develops compressive strength suitable for use in subterranean applications. While a hydraulic composition is one type of sealant composition that may be used in cementing methods, other non-hydraulic sealant compositions also may be employed. By way of example, polymeric sealant compositions also may be used.
Sealant compositions may be used in primary-cementing operations whereby pipe strings, such as casing and liners, are cemented in well bores. In performing primary cementing, a sealant composition may be pumped into an annulus between a subterranean formation and the pipe string disposed in the subterranean formation or between a pipe string and a larger conduit in the subterranean formation. The sealant composition should set in the annulus, thereby forming an annular sheath of hardened cement (e.g., a cement sheath) that supports and positions the pipe string in the well bore and bonds the exterior surface of the pipe string to the walls of the well bore.
Sealant compositions also may be used in remedial-cementing operations, such as sealing voids in a pipe string or a cement sheath. As used herein the term “void” refers to any type of space, including fractures, holes, cracks, channels, spaces, and the like. Such voids may include: holes or cracks in the pipe strings; holes, cracks, spaces, or channels in the cement sheath; and very small spaces (commonly referred to as “microannuli”) between an interior surface of the cement sheath and the pipe string or between the exterior surface of the cement sheath and the formation or a larger conduit. Sealing such voids may prevent the undesired flow of fluids (e.g., oil, gas, water, etc.) and/or fine solids into, or from, the well bore. The sealing of such voids, whether or not made deliberately, has been attempted by introducing a sealant composition into the void and permitting it to remain therein to seal the void. If the substance does not fit into the void, a bridge, patch, or sheath may be formed over the void to possibly produce a termination of the undesired fluid flow. Hydraulic pressure may be employed to force the sealant composition into the void. Once placed into the void, the sealant composition may be permitted to harden.
Remedial-cementing operations also may be used to seal portions of subterranean formations or portions of gravel packs. The portions of the subterranean formation may include permeable portions of a formation, fractures (natural or otherwise) in the formation, and other portions of the formation that may allow the undesired flow of fluid into, or from, the well bore. The portions of the gravel pack include those portions of the gravel pack, wherein it is desired to prevent the undesired flow of fluids into, or from, the well bore. A “gravel pack” is a term commonly used to refer to a volume of particulate materials (such as sand) placed into a well bore to at least partially reduce the migration of unconsolidated formation particulates into the well bore. While screenless-gravel-packing operations are becoming more common, gravel-packing operations commonly involve placing a gravel-pack screen in the well bore neighboring a desired portion of the subterranean formation and packing the surrounding annulus between the screen and the well bore with particulate materials that are sized to prevent and inhibit the passage of formation solids through the gravel pack with produced fluids. Among other things, this method may allow sealing of the portion of the gravel pack to prevent the undesired flow of fluids without requiring the gravel pack's removal.
Sealant compositions also may be used during the drilling of the well bore in a subterranean formation. For example, in the drilling of a well bore, it may be desirable, in some instances, to change the direction of the well bore. In some instances, sealant compositions may be used to facilitate this change of direction, for example, by drilling a pilot hole in a hardened mass of cement, commonly referred to as a “kickoff plug,” placed in the well bore. Certain formations may cause the drill bit to drill in a particular direction. For example, in a vertical well, this may result in an undesirable well bore deviation from vertical. In a directional well (which is drilled at an angle from vertical), after drilling an initial portion of the well bore vertically, the direction induced by the formation may make following the desired path difficult. In those and other instances, special directional drilling tools may be used, such as a whipstock, a bent sub-downhole motorized drill combination, and the like. Generally, the directional drilling tool or tools used may be orientated so that a pilot hole is produced at the desired angle to the previous well bore in a desired direction. When the pilot hole has been drilled for a short distance, the special tool or tools are removed, if required, and drilling along the new path may be resumed. To help ensure that the subsequent drilling follows the pilot hole, it may be necessary to drill the pilot hole in a kickoff plug, placed in the well bore. In those instances, prior to drilling the pilot hole, a sealant composition may be introduced into the well bore and allowed to set to form a kickoff plug therein. The pilot hole then may be drilled in the kickoff plug, and the high strength of the kickoff plug helps ensure that the subsequent drilling proceeds in the direction of the pilot hole.
Sealant compositions (e.g., hydraulic compositions) used heretofore may comprise Portland cement. Portland cement generally is a major component of the cost for the sealant compositions. To reduce the cost of such sealant compositions, other components may be included in the sealant composition in addition to, or in place of, the Portland cement. Such components may include fly ash, slag cement, shale, metakaolin, zeolite, and the like. “Fly ash,” as that term is used herein, refers to the residue from the combustion of powdered or ground coal, wherein the fly ash carried by the flue gases may be recovered, for example, by electrostatic precipitation. “Slag,” as that term is used herein, refers to a granulated, blast furnace by-product formed in the production of cast iron and generally comprises the oxidized impurities found in iron ore. Slag cement generally comprises slag and a base, for example, such as sodium hydroxide, sodium bicarbonate, sodium carbonate, or lime, to produce a hydraulic composition that, when combined with water, may set to form a hardened mass.
Once set, the hardened settable composition (e.g., the cement sheath) may be subjected to a variety of cyclic, shear, tensile, impact, flexural, and/or compressive stresses that may lead to failure of the cement sheath. Such failure may be the result of fractures, cracks, and/or debonding of the sheath from the pipe string and/or the formation. Undesirably, cement-sheath failure may lead to loss of zonal isolation, resulting, for example, in the undesirable migration of fluids between formation zones. This may lead to undesirable consequences such as lost production, costly remedial operations, environmental pollution, hazardous rig operations resulting from unexpected fluid flow from the formation caused by the loss of zonal isolation, and/or hazardous production operations. Furthermore, failure of the cement sheath also may be caused by forces exerted by shifts in subterranean formations surrounding the well bore, cement erosion, and repeated impacts from the drill bit and the drill pipe. Additives may be included in the settable composition to improve the mechanical properties and thus reduce sheath failure. However, these additives are often expensive and can undesirably increase the cost of the cementing operation.